this week president obama puts syrian leader bahsar al assad on notice about the use of chemical weapons. and now we know why. pentagon sources tell nbc news that syria is preparing chemical weapons for the possible use against the military people in the form of aerial bombs. jim miklaszewski reports. >> reporter: as the fighting grows more intense and syrian rebels close in on damascus, the syrian regime has turned increasingly desperate. u.s. officials tell nbc news the syrian military loaded the precursor chemicals for sarn nerve gas into aerial bombs. that could be dropped from dozens of syrian fighter bombers. this week u.s. intelligence detected a flurry of activity at chemical weapons sites like this one. while u.s. officials confirm the precursor chemicals are loaded, they must still be mixed together to create the deadly sarin gas. the development shook the world. president obama and secretary of state hillary clinton issued strong warnings to syria's president assad that there would be serious consequences if he used chemical weapons. >> it's the point of no return. they're goi